JPH04311931A - Manufacture of wavelength converting optical element - Google Patents

Abstract

PURPOSE:To enable a waveguide route layer arranged on a LiNbO3 substrate to be simply formed in a short time as well as to enable width cut of the waveguide route layer to be sharply carried out. CONSTITUTION:In a manufacturing method to manufacture a wavelength converting optical element by carrying out proton exchange on a LiNbO3 substrate 21 so as to provide an optical waveguide route layer 22 having higher refractive index than this substrate 21, this method has a characteristic that after solution containing elements capable 6f proton exchange, for example, pyrophosphoric acid (H4P2O7) solution 26 is applied to the substrate 21, a laser beam having wavelength shorter than absorption end wavelength of the substrate 21, for example, an EXICIMER laser beam 28 is radiated for several minutes to an area in which the optical waveguide route layer 22 is formed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a wavelength conversion optical element for obtaining a short wavelength light source used for optical information processing, optical measurement, etc.

0002

2. Description of the Related Art In recent years, short wavelength coherent light sources have been developed for application to high-density optical disk systems, measurement and display systems, and the like. In an optical disc system, the spot diameter of the light focused on the disc surface is proportional to the wavelength of the light source, so a short wavelength light source is essential to achieve high density.

As a short wavelength light source, semiconductor lasers have the advantages of being small, lightweight, and low power consumption, so the development of shorter wavelength lasers using new materials is progressing.
InGaA, which already has an oscillation wavelength in the 0.6 μm band (red)
1P semiconductor lasers have reached the level of practical use. However, although research has been carried out on green or blue semiconductor lasers with shorter wavelengths, no laser that can continuously emit light at room temperature has been obtained, and there is still no prospect of practical use.

On the other hand, as another means of realizing a short wavelength light source, optical second harmonic generation (SH) using a nonlinear optical crystal has been proposed.
G), and more research has been conducted than before. In order to realize compactness and low power consumption, attempts have been made to use a semiconductor laser as a fundamental wave light source and to turn a nonlinear optical crystal into a waveguide. For example, using a proton-exchanged LiNbO3 waveguide as shown in Fig. 7, , a 1 mW blue light source was obtained as the optical second harmonic of an 80 mW semiconductor laser (Taniuchi et al.; Autumn 1988 Applied Physics Society, 19p-Z
G-4 (1987)).

[0005] This method uses Cerenkov radiation to
It radiates harmonics into the waveguide substrate, which is similar to the conventional SH
Unlike the G method, this method has the advantage of not requiring phase matching through angle control, temperature control, etc. When creating a Cerenkov-emitting wavelength-converted laser, optically polished

0006
]A SiO2 film of several hundred nm is formed on the LiNbO3 (Z) plate using a sputtering device, or a Ta film is deposited to a thickness of 30 nm using electron beam evaporation, and then a resist is applied on these thin films and patterned using a photo process. conduct. Then,

[0007] These films are patterned by wet etching in a HN3 F solution in the case of a SiO2 film, and dry etching in a CF4 gas in the case of a Ta film, using a resist as a mask. Next, after removing the resist, pyrophosphoric acid was applied on the Z surface and heated at 230°C.
A proton exchange (heat treatment) is performed for 5 to 10 minutes in an electric furnace to remove the SiO2 film and Ta film by etching to form a device. Note that the SiO2 film was etched with HN3F solution at room temperature, and the Ta film was etched with NaOH.
It is carried out at 70°C in a solution of the system.

However, this type of method has the following problems. In other words, since waveguide formation is achieved using the process described above, complicated processes such as thin film formation, resist patterning, selective etching of the thin film, proton exchange, and thin film removal are required, and the process is time-consuming. It takes. Furthermore, there were other problems such as poor cutting of the width of the obtained waveguide.

[0009] As another method, ion exchange KTi
There is an example using an OPO4 (KTP) crystal waveguide. K
TP crystal is currently considered to be the most excellent crystal as an SHG material for YAG lasers. Moreover, it has features such as a high laser damage threshold, no hygroscopicity and thermal stability, and small temperature change in refractive index and good temperature characteristics. on the other hand,
The difficulty is that the SHG is 0.53 μm due to phase matching.
Light generation is limited to short wavelengths, and in order to achieve compact size and low power consumption, a semiconductor laser cannot be used as a fundamental wave light source. Furthermore, conventional ion exchange is performed using relatively high temperatures of 350 to 450° C. and requires post-annealing. For this reason, there were problems such as the process being complicated and the crystal itself deteriorating.

0010

[Problems to be Solved by the Invention] As described above, in the past, Li
In the method of manufacturing a wavelength conversion optical element using NbO3 crystal, it is necessary to use a complicated process, so there are problems that the manufacturing process is time-consuming and the width of the obtained waveguide is poor. Further, a similar problem occurred when KTP crystal was used. The present invention has been made in consideration of the above circumstances, and its purpose is to:

00
11] To provide a method for manufacturing a wavelength conversion optical element, which allows a waveguide layer to be provided on a LiNbO3 substrate or a KTP substrate to be easily and easily created in a short time, and also allows sharp cuts in the width of the waveguide layer. It is in.

0012

[Means for Solving the Problems] The gist of the present invention is to perform heat treatment in proton exchange or ion exchange using a short wavelength laser such as an excimer laser.

That is, the present invention provides a method for manufacturing a wavelength conversion optical element in which ion exchange is performed on a KTiOPO4 substrate and an optical waveguide layer having a higher refractive index than the substrate is provided, in which a solution containing an element to be ion-exchanged is placed on the substrate. After coating the substrate, the region where the optical waveguide layer is to be formed is irradiated with a laser beam having a wavelength shorter than the absorption edge wavelength of the substrate.

The present invention also provides a method for manufacturing a wavelength conversion optical element in which proton exchange is performed on a LiNbO3 substrate and an optical waveguide layer having a higher refractive index than the substrate is provided, in which a solution containing an element to be proton exchanged is placed on the substrate. After coating the substrate, the region where the optical waveguide layer is to be formed is irradiated with a laser beam having a wavelength shorter than the absorption edge wavelength of the substrate.

[0015]

[Operation] According to the present invention, the surface of a substrate coated with a solution containing an element to be ion-exchanged or proton-exchanged is irradiated with laser light (for example, excimer laser light) having a wavelength shorter than the absorption edge wavelength of the substrate. Therefore, annealing is performed to a predetermined depth from the substrate surface, and ion exchange or proton exchange can be performed only on the portion irradiated with the laser beam. In this case, unlike the case where the entire substrate is subjected to heat treatment, a photo process, a subsequent etching process, etc. are not necessary. Furthermore, since irradiation with excimer laser light or the like can be performed at room temperature, there is no need to heat the substrate. Therefore,
In addition to simplifying the process and shortening the manufacturing time, it is possible to almost eliminate damage to the crystal substrate. Furthermore, since local annealing is performed and the elapsed process time is short, it is possible to sharply cut the width of the waveguide layer.

[0016]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing a schematic configuration of a wavelength conversion optical element according to a first embodiment of the present invention. 1 in the diagram
1 is a LiNbO3 crystal substrate (nonlinear optical crystal), and a part of this crystal substrate 11 has a waveguide section (optical waveguide layer).
12 are formed in a stripe shape. The waveguide section 12 is
It is formed by substituting Li and H in a nonlinear optical crystal using a proton exchange method, and this waveguide section 12 is covered with crystal substrates 11 on three sides. Here, the cross-sectional shapes of the crystal substrate 11 and the waveguide section 12 are both rectangular. In such a configuration, the waveguide 12 receives external excitation light (input light) with a wavelength of approximately

By irradiating the semiconductor laser beam 13 with a wavelength of 0.9 μm, a fundamental wave 14 having the same wavelength as the input light 13 and an optical second harmonic (blue laser beam with a wavelength of approximately 0.45 μm) are generated.
15 occurs. The input laser beam 13 is output as a fundamental wave 14 from the end of the mirrored waveguide 12, and the optical second harmonic 15 is output as short wavelength light from the end of the crystal substrate 11. By utilizing this optical second harmonic 15, it is possible to realize a light source with a shorter wavelength that cannot be realized with a semiconductor laser. Next, a method for manufacturing the wavelength conversion optical element shown in FIG. 1 will be described with reference to FIG. 2.

First, as shown in FIG. 2(a), on the upper surface (Z plane) of the LiNbO3 flat plate 21 of the nonlinear optical crystal,
For example, a pyrophosphoric acid (H4 P2 O7) melt 26 is applied thinly. At this time, spin coating may be used. Next, as shown in FIG. 2(b), a glass mask (line width 5 μm) 27 is placed so as to be in close contact with the surface coated with this solution 26, and as shown in FIG. 2(c), a glass mask 27
Excimer laser light (wavelength: about 0.193 μm, power: 10 W) 28 is irradiated for several minutes through the filter to perform proton exchange. Here, the excimer laser beam 28 (for example, ArF:
Wavelength 193nm) is

Since the wavelength is shorter than the absorption edge wavelength of LiNbO3, the excimer laser beam 28 irradiated onto the substrate crystal 11 reaches a certain depth from the substrate surface and anneals the crystal substrate 11 from the surface to that depth. At this time, since the aforementioned melt 26 is applied to the substrate surface, proton exchange between Li and H is performed in the annealing portion.

By the above proton exchange, a layer 22 having a different refractive index is formed on the portion of the flat plate 21 other than the mask, as shown in FIG. 2(d). This constitutes the waveguide section 12. After this, the glass mask 27 is removed, the flat plate 21 is washed with water, and if necessary, the waveguide 1
The end face including 2 is mirror-processed. By cutting out individual elements, the structure shown in FIG. 1 is realized.

When the wavelength conversion optical element thus obtained is irradiated with semiconductor laser light 13, H+ (protons) and Li
An optical second harmonic wave 15 is generated through the waveguide section 12 in which . This makes it possible to obtain blue laser light with a wavelength of about 0.45 μm from the end of the optical element of this example.

FIG. 3 shows the results of measuring surface scattering (light loss) by irradiating the wavelength conversion optical element thus obtained with semiconductor laser light. A shows the one obtained in this example, and b shows the one formed through the conventional PEP and heat treatment process for comparison. It can be seen that the optical loss of the wavelength conversion optical element a obtained this time is suppressed to about 1/3 compared to the conventional wavelength conversion optical element b. This also relates to the output power of the optical second harmonic, and therefore the relationship with the output power is shown in FIG. A and B are the respective wavelength conversion optical elements used above. From FIG. 4, it can be seen that the output power of A is approximately twice as strong as that of B.

[0024] When creating an optical element, unlike those created using conventional processes, the unevenness of the pattern edge is small (conventionally it is ±50 nm, and this one is ±15 nm).
), the light loss on the surface can be reduced accordingly, and the light can be extracted to the outside better. Furthermore, this is thought to be due to the fact that a uniform layer was obtained without temperature unevenness due to heat treatment.

As described above, according to this embodiment, in the process of creating a waveguide section of a conventional waveguide type wavelength conversion optical element, a solution is applied to the crystal surface, a mask is brought into close contact with the surface, and an excimer laser is applied through the mask. By irradiating with light, it is possible to reduce the unevenness of the pattern edge of the waveguide width, and moreover, it is possible to form an optical waveguide layer that is more homogeneous than heat treatment. Therefore, a wavelength conversion optical element with low loss and high wavelength conversion efficiency can be realized at low cost.

FIG. 5 is a diagram showing a schematic configuration of a wavelength conversion optical element according to a second embodiment of the present invention. In the figure, reference numeral 51 denotes a KTiOPO4 (KTP) crystal substrate as a nonlinear optical crystal, and a waveguide section (optical waveguide layer) 52 is formed in a stripe shape on a part of this crystal substrate 51. The waveguide section 52 is formed by substituting K and Rb in a nonlinear optical crystal using an ion exchange method, and the waveguide section 52 is covered with crystal substrates 51 on three sides. Here, the crystal substrate 51
The cross-sectional shapes of the waveguide portion 52 and the waveguide portion 52 are both rectangular.

Even in such a configuration, when the semiconductor laser beam 53 with a wavelength of about 0.9 μm is irradiated to the waveguide 52 as external excitation light (input light), the optical wave 53 and the fundamental wave 54 having the same wavelength as the input light 53 are generated. A second harmonic (blue laser with a wavelength of approximately 0.45 μm) 55 is generated. Then, the input laser beam 53
The fundamental wave 54 is transmitted from the end of the mirror-processed waveguide 52.
The optical second harmonic 55 is output as short wavelength light from the end of the crystal substrate 51. Next, a method for manufacturing the wavelength conversion optical element shown in FIG. 5 will be described with reference to FIG. 6. First, as shown in Fig. 6(a), the nonlinear optical crystal KTP
The top surface of the flat plate 61 of

A rubidium chloride aqueous solution 66 containing Rb is applied thinly to the (Z surface). Next, as shown in FIG. 6(b), a glass mask 67 is placed on the surface coated with the solution 66 so as to be in close contact with the surface. Next, as shown in FIG. 6(c), the excimer laser beam 6 is passed through the glass mask 67.
8 to perform ion exchange of K and Rb.

As a result, as shown in FIG. 6C, a layer 62 having a different refractive index is formed on the portion of the flat plate 61 other than the mask, and this constitutes the waveguide section 52. Next, as shown in FIG. 6(d), the mask 67 is removed,
By washing away the aqueous solution 66 by washing with water or the like, the structure shown in FIG. 5 is realized.

When the wavelength conversion optical element thus obtained is irradiated with semiconductor laser light 53, a second harmonic wave 55 of light is generated through the waveguide 52 containing Rb.
The harmonics 55 are emitted from the ends of the crystal substrate 51. Therefore, similarly to the previous embodiment, it is possible to obtain blue laser light with a wavelength of approximately 0.45 μm from the end of the wavelength conversion optical element.

As described above, according to this embodiment, it is possible to realize a blue laser using a KTP crystal, which was previously considered impossible. That is, short wavelength laser light (blue) can be generated simply by irradiating excitation light onto the waveguide section 52 in which K is replaced with Rb. Furthermore, it has the advantage that it can be realized through an extremely simple process of simply ion-exchanging Rb into the waveguide of a conventional waveguide-type wavelength conversion element by irradiating it with excimer laser light.

It should be noted that the present invention is not limited to the above-mentioned embodiments. In the first embodiment, pyrophosphoric acid was used as the solution, but a phosphoric acid solution containing Deutron (D) can also be used. In the second example, rubidium chloride was used as the Rb-containing aqueous solution, but the present invention is also applicable to cases where other aqueous solutions of rubidium carbonate and rubidium azide are used. Further, although glass was used as the mask material, there is no problem if the mask is made of metal. Furthermore, the mask is used to selectively irradiate the substrate surface with laser light for ion exchange or proton exchange, and if the laser light is selectively irradiated in the form of a spot, the mask can be omitted. be. In addition, various modifications can be made without departing from the gist of the present invention.

[0033]

Effects of the Invention As detailed above, according to the present invention, by performing heat treatment in proton exchange or ion exchange with short wavelength light such as an excimer laser, LiNbO3 substrate or

[0034] It is possible to realize a wavelength conversion optical element in which an optical waveguide provided on a KTP substrate can be easily produced in a short time, and the width of the waveguide can be sharply cut.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a schematic configuration of a wavelength conversion optical element according to a first embodiment of the present invention;

FIG. 2 is a sectional view showing the manufacturing process of the first embodiment;

[Figure 3
]A characteristic diagram showing the relationship between crystal length and optical loss of the first example,

FIG. 4 is a characteristic diagram showing the relationship between input power and output power of the first embodiment;

FIG. 5 is a perspective view showing a schematic configuration of a second embodiment of the present invention;

FIG. 6 is a perspective view showing the manufacturing process of the second embodiment;

[Figure 7
] A perspective view for explaining a conventional wavelength conversion optical element.

[Explanation of symbols] 11...LiNbO3 crystal (nonlinear optical crystal), 12,
52... Waveguide (optical waveguide layer), 13,53... Input light, 14,54... Fundamental wave, 15,55... Optical second harmonic, 21,61... Flat plate, 26... Pyrophosphoric acid (H4 P2 O7) Melt 27,6
7... Glass mask, 28, 68... Excimer laser light, 51... KTP crystal (nonlinear optical crystal), 66... Rubidium chloride aqueous solution.

Claims (2)

[Claims] 1. A method for manufacturing a wavelength conversion optical element in which ion exchange is performed on a KTiOPO4 substrate and an optical waveguide layer having a higher refractive index than the substrate is provided, wherein a solution containing an element to be ion-exchanged is applied onto the substrate. A method for manufacturing a wavelength conversion optical element, comprising the steps of: irradiating a region where the optical waveguide layer is to be formed with a laser beam having a wavelength shorter than the absorption edge wavelength of the substrate. 2. A method for manufacturing a wavelength conversion optical element in which proton exchange is performed on a LiNbO3 substrate and an optical waveguide layer having a higher refractive index than the substrate is provided, wherein a solution containing an element to be proton exchanged is applied onto the substrate. A method for manufacturing a wavelength conversion optical element, comprising the steps of: irradiating a region where the optical waveguide layer is to be formed with a laser beam having a wavelength shorter than the absorption edge wavelength of the substrate.